Three-dimensional (“3D”) graphics processing pipelines perform a series of steps to convert input geometry into a two-dimensional (“2D”) image for display on a screen. Some of the steps include rasterization and pixel shading. Rasterization involves identifying which pixels (or sub-pixel samples) are covered by triangles provided by stages of the pipeline prior to the rasterizer. The output of rasterization includes quads—a block of 2×2 pixels—and coverage data that indicates which samples are covered by the pixels of the quads. The pixel shader shades the pixels of the quads, and the pixels of the quads are then written to a frame buffer. Because pixel shading is very resource-intensive, techniques are constantly being developed to improve efficiency of pixel shading.